During travel of an engine-powered vehicle, there are many instances when the vehicle must stop before a destination is reached. This may occur, for example, when the vehicle stops at traffic signals, cross-walks, stop signs and the like. A micro-hybrid vehicle may enable a stop/start strategy for starting and stopping the vehicle engine during a driving event. The engine is shutdown if no power is required (e.g. while waiting at a traffic light). As soon as power is requested, the engine is automatically restarted. By avoiding unnecessary engine idling, the vehicle's fuel economy will be improved. For this reason, it is desirable to use the engine shutdown function as much as possible when certain engine stop conditions are satisfied.
A micro-hybrid having a start/stop engine may use a number of factors to determine when to shutdown and restart the engine to achieve the goal of reducing fuel consumption and emissions while the vehicle is stationary. Typically, the engine is shutdown when wheel speed is zero and the brake pedal is depressed. Other considerations may include the engine coolant temperature, battery state of charge, fuel rail pressure, A/C operation, and others that may be used to prevent an engine shutdown and/or to initiate an engine restart. Physical limits of the start/stop system associated with engine/transmission inertia, starter design, combustion control limits, etc., may also impose constraints on the time required to shutdown and restart the engine. This time may adversely impact vehicle launch performance after an engine shutdown, particularly in vehicles with an automatic transmission. As such, it is desirable in some cases to avoid shutting the engine off, or restarting the engine in anticipation of a vehicle launch to improve launch performance.